Vietnam is requiring major state-owned companies to sell all their foreign currency to banks, according to a report on a government website on Thursday, in an effort to support the beleaguered dong.

The dong has been under persistent downward pressure in the past three years due to high inflation and wide trade and fiscal deficits, and the central bank has devalued the official exchange rate by more than 20 percent.

Prime Minister Nguyen Tan Dung approved a series of measures on Thursday to tighten monetary and fiscal conditions to control inflation and re-balance the economy, after a devaluation and interest rate rises earlier this month.

Dung told an online meeting about the economy with the heads of Vietnam's 63 provinces and municipalities on Thursday that "immediately following the meeting, definitely all state-owned groups and general corporations will have to sell all foreign currency to banks".

Banks would sell them dollars at the official exchange rate when they need them, he said, according to the report on the government's website, www.chinhphu.vn.

The currency was quoted at a major gold shop in Hanoi at VND22,000/22,100 per dollar at about 0940 GMT. The rate has eased on the unofficial market from about 22,500 last weekend.